Aircraft: M-20 SERIES UNDIFFERENTIATED OR OTHER MODEL
Phase of flight: Final Approach
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Critical

I was working Local Control 1/Local Control 2 with high complexity due to construction closures and vehicles occasionally calling for clearances. Runway 11R and Runway 2/20 were closed to allow painting to occur; so Runway 11L was the single active runway for fixed wing aircraft. Traffic volume was increasing with multiple departures and aircraft inbound that were requesting pattern work to the single runway; with occasional helicopter operations. I remember that I had a Mooney inbound on a left base to 11L; with other inbounds and at least two other aircraft in the pattern for 11L; including a Skyhawk. There seemed to be multiple requests for additional services that I felt added to frequency congestion and made the situation more complex and frustrating at times. I honestly do not recall working this level of traffic in awhile to a single runway; so I was definitely 'rusty' for this operation. But I felt that I needed to take advantage of the situation to push some traffic to maintain my skills and controlling ability. I recall that my initial plan was to have another Mooney depart prior to the second Mooney arrival and communicated this to the arriving Mooney before clearing him to land. I also advised the Skyhawk to extend downwind to make room for the two departures; and that I would call his base turn. However; the Skyhawk did not appear to continue downwind and instead turned base from a position that would not allow space for the departures; and could conflict with the Mooney. When I told the Skyhawk to turn out to the west and square his base (reminding him that I said I would tell him when to turn base); I believe I lost awareness of where the Mooney was on final; and instead told a Skylane of the position of the Mooney upwind as I cleared him for take off without remembering that the Mooney was so close in on final! I thought I had a hole for the departure; but I did not. I saw the inbound Mooney short final and immediately issued a go around that was acknowledged by the pilot as he began a climb. After the Skylane was established upwind; he acknowledged that he had the Mooney ahead in sight. After the incident; I took steps to regain control of the pattern by restricting pattern work and holding aircraft outside Class D until I was confident that I regained full awareness of my traffic situation. In hindsight; I needed to take steps earlier to gain greater control of the pattern as traffic was building. This event is a sobering learning experience about my own personal signs of overload developing; and I will apply these personal lessons learned in the future. The bottom line was my scan; my scan of strip bays and out the window broke down and I lost situational awareness of the position of the Mooney on final. I fell behind the volume of traffic that was inbound to the airport at that time; and allowed a pilot's miscue (unplanned early base turn) distract me into inadvertently issuing a badly timed take off clearance. Tower Controller described a very busy/complex traffic situation that resulted in a go around; the reporter noting multiple factors and distractors leading to the event.